Superconductors are capable of expressing a superconducting phenomenon in which an electrical resistance becomes zero at an extremely low temperature and causing a large current to flow as compared to typical conductors such as a copper wire, and thus, superconducting coils obtained by processing a wire member as a superconductor in a coil shape can be used as a strong electromagnet. The superconducting coils have been used for, for example, a medical diagnostic device such as MRI (magnetic resonance imaging), a scientific measurement device such as NMR (nuclear magnetic resonance), a linear motor type magnetic levitation train, and the like.
As an example of the above-described superconducting coils, known is a coil that is provided with a winding portion in which a superconducting conductor, formed using a thin film-like superconducting wire obtained by stacking an intermediate layer, a superconducting layer, and a stabilized metal layer on one face of a metal substrate, is wound around a circumferential face of a cylindrical shape winding frame (see PTL 1 to be described later). In this superconducting coil, the superconducting conductor is co-wound with a stabilizing material formed using a metal tape, and the stabilizing material is arranged at least at an inner diameter side of the superconducting conductor. The superconducting conductor is wound such that a face of the stabilized metal layer and a face of the metal substrate become the inner diameter side and an outer shape side, respectively.
A persistent current switch including a non-inductive superconducting coil, for example, is used for opening and closing a persistent current circuit (see PTL 2 to be described later). Such a persistent current switch is formed using a conductor which can be switched in any direction between a superconducting state and a normal conducting state by setting an environment condition, for example. This conductor is turned into a switch-on state in the superconducting state as an electrical resistance becomes zero and current flows without being attenuated, and a switch-off state is practically realized when the conductor is switched to the normal conducting state and the electrical resistance increases.